This invention is directed to optical devices. More specifically, embodiments of the invention provide LED packaging having reflector surfaces, and in some implementations provide LED packages that include thermal pad structures for dissipating heat generated by the LED devices. In particular, thermal pad structures with large surface areas are used to provide heat transfer. In certain embodiments, thick thermally conductive material is used to improve overall thermal conductivity of an LED package, thereby allowing heat generated by LED devices to dissipate quickly. Depending on the application, thermal pad structure, thick thermal conductive layer, and reflective surface may be individually adapted in LED packages or used in combinations.
In the late 1800's, Thomas Edison invented the light bulb. The conventional light bulb, commonly called the “Edison bulb,” has been used for over one hundred years. The conventional light bulb uses a tungsten filament enclosed in a glass bulb sealed in a base, which is screwed into a socket. The socket is coupled to an AC power or DC power source. The conventional light bulb can be found commonly in houses, buildings, and outdoor lightings, and other areas requiring light. Unfortunately, the conventional Edison light bulb dissipates much thermal energy. More than 90% of the energy used for the conventional light bulb dissipates as thermal energy. Additionally, the conventional light bulb eventually fails due to evaporation of the tungsten filament.
Fluorescent lighting overcomes some of the drawbacks of the conventional light bulb. Fluorescent lighting uses an optically clear tube structure filled with a noble gas, and typically also contains mercury. A pair of electrodes is coupled between the gas and to an alternating power source through a ballast. Once the mercury has been excited, it discharges to emit UV light. Typically, the optically clear tube is coated with phosphors, which are excited by the UV light to provide white light. Many buildings use fluorescent lighting and, more recently, fluorescent lighting has been fitted onto a base structure, which couples into a standard socket for household use.
Solid state lighting techniques have also been developed. Solid state lighting relies upon semiconductor materials to produce light emitting diodes, commonly called LEDs. At first, red LEDs were demonstrated and introduced into commerce. Modern red LEDs use Aluminum Indium Gallium Phosphide or AlInGaP semiconductor materials. Most recently, Shuji Nakamura pioneered the use of InGaN materials to produce LEDs emitting light in the blue color range for blue LEDs. The blue LEDs led to innovations such as solid state white lighting, the blue laser diode, which in turn enabled the Blu-Ray™ DVD player (trademark of the Blu-Ray Disc Association), and other developments. Blue, violet, or ultraviolet-emitting devices based on InGaN are used in conjunction with phosphors to provide white LEDs. Other colored LEDs have also been proposed.
To take advantage of LED devices, well designed LED packages that house LED devices and provide electrical connections are essential. Numerous types of conventional LED packages have been used, however, they suffer from various disadvantages.